Documentation:SBME-Teaching-Labs/Soldering and Electronics

Tips for Producing Good Electronic Circuits

Tip 1: Whenever possible, use a soldered or crimped connection. This will ensure a solid, movement resistant joint which is less likely to fail. Always be sure to cover any exposed conductor with heat shrink or electrical tape.

Tip 2: Always check the limits of your microcontrollers. Micros will have a specified total, and pin specific, current/voltage limit. Do not exceed this limit or it may damage your microcontroller. Excessive current may be caused by shorts, or other direct paths to a dead-ground. If you need a larger current than can be safely supplied by the micro, try using a transistor as a current amplifier. External current limiting resistors can always be used to control current flow through a circuit line as well. Lastly, do not put too heavy a load on a pin or controller by using too many high-requirement components such as sensors. At some point, the controller will not be able to properly power the components and you will receive degraded or no signals back. Try using external power sources and just controlling the sensors with the microcontroller.

Tip 3: Whenever you are connecting wires to header pins on a microcontroller, there will be no easy way to form permanent connections (though it can be done). Instead of feeding stripped wires directly into the header pins, try adding a Dupont connector to the end of the wire and then inserting this into the header pin. This will create a much more reliable connection than the bare wire (it will also last longer).

Tip 4: For motors and other inductive components, be aware of the effects these have on your larger circuit. Electric motors have a few main effects than can cause circuit damage. One such effect is back-EMF. Back-EMF is a voltage generated which opposes the supply voltage. It is created by the spinning of the coils through the motors magnetic field. During use, it is not much of an issue, but when decelerating or stopping the motor, the sudden lack of applied supply voltage causes the back-EMF to spike, resulting in a large voltage in the direction opposite of intended. This can result in over-voltage and over-current in your circuit which may damage components. There are several options you can explore, including flyback diodes and braking modes on motor drivers. In-rush current with motors is also related to back-EMF. With the initial lack of back-EMF from the motor being off, when the circuit / motor is first started, you can see a quick, large rise in current. Thermistors, resistors, diodes, and smart soft-start (voltage ramping) techniques, can be used to limit this effect as well.

Tip 5: Color code your wires! Follow a standard convention. Make all power lines red and ground black. For non-standard wires, decide and record your own convention. As an example, white carries the signal, blue is for clock signals from the controller, and green is for chip to chip communication.

Soldering and Electronics

Soldering Equipment

The makerspace has various soldering irons and the associated equipment and consumables. For information on how to effectively solder, please see below. Please note that all soldering, regardless of type, must be completed under a running ventilation hood to prevent toxic smoke inhalation.

Methods of Soldering

See this document here for a breakdown of the different soldering methods.

Removing Solder

Methods to Remove Solder from a Joint

There are 2 mains ways to remove solder from a joint, whether because of improper application or place, or to repair or replace parts. These include the use of a solder pump or solder wick.

Solder pumps are effectively small vacuums used to suck up solder. However, it must first be liquified through heating using a soldering iron, heat gun, or some other method. In the version shown here, the plunger is depressed and the nozzle placed on the joint you wish to remove solder from. Once the solder is liquified, the button on the side is pressed and the plunger will raise, lifting solder with it.

Solder wicks use a metallic strand to 'wick' liquid solder from a joint, pulling it into the solder wick itself. This does make it a consumable item however. To use the wick, place it over the soldered joint in question and heat the joint with a soldering iron, placing the wick between the iron and solder. As it liquifies, it will be pulled onto the wick, though you may need to move the wick around to remove all of the solder.

Types and Methods of Forming Electrical Connections

There are various methods of forming electrical connections between wires, ports, pins, etc. aside from soldering. In different cases, these alternative methods are easier and more secure than others. Some examples of alternatives include:

• Screw Terminals
• Crimp (Butt) Connectors
• Ring / Nut Connectors
• JST Connectors
• Spade Connectors

For a breakdown of these connectors and their uses, see below.

Crimp (Butt) Connectors

Butt Connectors

Commonly known as butt connectors, these connector types are characterized by a metal tube used to hold one or more wires in place. the metal tube is then crimped around the wire to prevent dislodging. These are fast and effective tools to connect wires with smaller diameters (general electrical wire gauges) in systems that will not be under much physical tension or vibration. When using them, be sure to further insulate the connection if using in electrically hostile environments with high moisture or corrosive elements to prevent both the wire and joint. Be aware these are permanent connections that cannot be reused or easily removed.

Ring \ Fork Connectors

Ring and Fork Connectors

Ring and fork connectors are used to provide a termination point to a wire which can be connected to a screw or bolt. As an example of this is the connection on your car battery positive and negative terminals. They are used similarly to butt connectors in that the wire is crimped into place within the housing. These connectors are easy to use and can be removed from the associated terminal post or screw easily. However, they can be prone to corrosion which affects the conductivity and reliability of the connection over long periods of time. Moreover, high vibration environments can dislodge the terminal as the screw or nut loosens over time without proper consideration, such as the use of anti-vibrational screws or locking nuts. To note, they do provide the added benefit of allowing multiple wires to be connected to one terminal post with the use of multiple ring or fork connectors.

Spade Connectors

Spade Male and Female Connectors

Spade connectors are a third type of crimp connector but have male and female ends. These ends connect to one another allowing for the adjoining wires to be disconnected or connected when needed. This may provide a less permanent solution than the above butt connectors, but also means it is possibly a less reliable connection, though still very strong. These should only be used in cases where wires may or will need to be repeatedly disconnected for some reason and should not be used for permanent connections when possible.

JST Connectors

JST Connectors

JST connectors are a specific type of quick connect housing and pin structure. They come in male-female pairs and different pin amounts (2-pin, 3-pin, 4-pin, etc.). They can be commonly seen in electronics and microcontroller work in breakout boards or sensors to allow for easy connection of accessories when testing or in cases when frequent part replacement may be necessary. While these connectors are adaptable, easy to use, and can provide a secure electrical connection, they are also susceptible to dust, debris, and corrosion. When adding these connectors to a circuit, the male connector may or may not come pre-installed with pins. If not, follow the same procedure as for the female side, but be sure to use the male components instead of the female. Regardless of male or female, JST connectors are comprised of 2 parts, the white plastic housing, and the metal tab which connects to the circuit or board. First, the wire is stripped and placed into the metal tab, which is then crimped around the wire. Be careful to accidentally crimp the spring pin used to keep the wire within the housing. Then the metal tab and wire are seated into the housing. If connecting to a circuit board, pins bent at a 90 degree angle are used instead of wires.

Dupont Connectors

Dupont Connectors

Dupont connects are very similar to JST connectors in structure but are meant for less permanent, prototyping applications and should not be a long term or permanent solution as they are prone to having poor electrical contact over time. The process for installing Dupont connectors (which are what is found on the ends of jumper cables) is also similar to JST. A metal tab (whether male or female) is crimped around a stripped wire and placed into a plastic housing. These housings come in multiple pin numbers.

Captive Screw Terminals

Captive Screw Terminal Block

Screw terminals are generally found on breakout boards or microcontrollers and allow a stripped wire to be clamped into place, forming an electrical connection. These terminals use pressure placed on a plate by a screw to form the electrical contact with the wire. They can be a bit tricky to install, but once installed allow for easy replacement of the wires feeding into them, allowing for rapid prototyping and switching of components. When properly installed and used, these connections are reliable and generally robust to higher voltages and currents (though you should always confirm its specific ratings), but can be susceptible to over-tightening and loosening with vibrations. Screw terminal blocks have different connect types on the non-screw fed end, and may need to be soldered into place.

Push-in / lever lock / WAGO connectors

Lever Lock Wire Connectors

Lever lock wire connectors (commonly referred to as WAGOs, though this is just a specific brand are used to simplify wire connection and can be seen used in some parts of world commonly for residential electrical work. These connector types are simple to use, provide good shielding from accidental connections, and allow for easy replacement of an individual wire. While providing a reliable and robust connection method, care must be taken to follow the proper instructions on wire gauge and strip length. To use these connectors, the stripped wire is inserted into the connector with the lever raised. The lever is then lowered, clamping down on the wire.

A Final Note on Connectors

In looking for the right connector for your work, you will come across an uncountable number of options beyond the common ones described here. Each type has its benefits and downsides. Be sure to do your research when selecting connectors regarding the type of physical and electrical environments they are intended for, especially as it relates to wire gauge and current and voltage carrying capacity. Do NOT overload your connectors with high voltage or current. It will damage your connector and likely your circuit as well.

Electrical Testing Equipment

The makerspace carries various electrical testing equipment for student use. This includes:

• Oscilloscopes
• Arbitrary Waveform Generators
• Programmable DC Power Supplies
• Multimeters
• EMF Detectors